1. Field of the Invention
The invention relates to novel compositions of matter which are useful for stripping or softening paint and methods for using such compositions. More particularly, the invention concerns paint removal compositions which are water-soluble and environmentally safe.
2. Description of the Prior Art
The term "paint remover" as hereafter applied refers to chemical compositions which can strip or facilitate stripping of coatings, such as, paint, lacquer, varnish, shellac, polyurethane finishes, enamels, and other coatings used to protect substrates and to beautify them. If applied by wiping, a paint remover can also serve to "degloss" a finish so that it will be suitably prepared for application of a new coat of paint. When used on brushes or other coating applicators, some paint removers can remove hardened paint and restore the brush to usable condition.
Chemical paint removers have achieved considerable popularity because they are much easier to use than the non-chemical alternatives of blow torches or power sanders. These chemical paint removers fall into two categories. One category is a caustic based remover which is seldom used in home applications because it is heated and requires dip tanks. This category has a deleterious effect on most kinds of wood, and often dissolves glue holding the furniture together.
The most popular type of paint remover incorporates an organic chemical solvent base. A typical composition of such a paint remover is disclosed in U.S. Pat. No. 2,507,983, methylene chloride constituting 86% by weight of the mixture and methanol usually being added in smaller proportion to solubilize a methylcellulose thickener. Paint removers based on methylene chloride are generally very effective on varnish and alkyd paint. They are less effective on lacquer and latex finishes. Unthickened removers which have high concentrations of methanol and benzene are used for varnish removal. Wax is sometimes added to restrain the rapid evaporation of the organic solvents.
A serious objection to such paint removers is their high degree of toxicity, particularly due to the inhalation of vapors. Another serious objection is that they can burn the skin causing various degrees of dermatitis, depending on the exposure.
A substantial body of literature directed to the extremely hazardous nature of methylene chloride has developed and it is clear that the use of this material in paint removers, while extensive in the past, must be discontinued.
Other hazardous chemicals have commonly been used in paint removers, such as, methanol, benzene, xylene, hydrogen peroxide, phenol and cresols, and the like. All of these materials are highly disadvantageous with respect to the environment or safety. The organic materials all are toxic to various degrees and others of the materials named are so highly corrosive or caustic that they can only be used under very restricted conditions.
One attempt to avoid the presence of the environmentally unsuitable methylene chloride or other organic solvents has been the inclusion in paint removers of N-methyl-2-pyrrolidone. Thus, U.S. Pat. No. 4,128,810 discloses the use of N-methyl-2-pyrrolidone in combination with a mixture of aromatic hydrocarbons having more than 6 carbon atoms. The composition exhibits better safety characteristics, low toxicity, low volatility and does not burn the skin and also operates as a paint remover. However, a major disadvantage of this composition is the fact that it is not water soluble.
A significant problem occurs in the painting of vehicles, e.g., automobiles and the like, wherein the parts for the automobiles are spray-painted in metal spraying booths. The interior of the booths must be cleaned, usually on a daily basis, and the paint on the surfaces of the interior of the booth, which is usually made of metal, removed. The use of a paint removal spray in such a situation is highly advantageous. However, it is understandable that the art is quite reluctant to utilize a paint remover containing the toxic materials outlined above. However, an additional problem is that if one uses a paint remover or stripper which is not water soluble, it is difficult to wash away the softened paint which, itself, of course, is not water soluble. Normally, it is desired, after application of the paint remover and allowing it to stand for a sufficient amount of time to soften the paint, to hose or brush the entire facility down. Paint removers containing the organic materials do not work satisfactorily when the booths are hosed down and are incompletely removed.
Attempts to produce paint removers which are water soluble generally require the presence of highly corrosive materials, such as, alkali metal hydroxides. Typical of such materials is the composition disclosed in U.S. Pat. No. 4,368,082. Clearly, the corrosive nature of such materials not only creates safety hazards, but also can be destructive to the substrate from which the paint is being removed.